Acquired Cystic Disease-Associated Renal Cell Carcinoma Extending to the Renal Pelvis Mimicking Urothelial Carcinoma on Computed Tomography (CT): Two Case Reports.

BACKGROUND Acquired cystic disease-associated renal cell carcinoma (ACD-associated RCC), which was added to the 2016 World Health Organization classification, is the most common subtype of RCC in patients undergoing long-term dialysis. ACD-associated RCC is underrecognized and reports of computed tomography (CT) and magnetic resonance imaging findings for the lesion are sparse. Similar to urothelial carcinoma, ACD-associated RCC is poorly to slightly enhanced on dynamic CT. Here, we report 2 cases of ACD-associated RCC filling the renal pelvis and mimicking urothelial carcinoma. CASE REPORT We describe 2 cases of ACD-associated RCC filling the left renal pelvis in patients undergoing dialysis for more than 10 years. In both cases, the patient's chief complaint was hematuria, and a left renal pelvic mass with poor enhancement was seen on dynamic CT. In both cases, the preoperative diagnosis was urothelial carcinoma of the left renal pelvis. Total nephroureterectomy was performed, and the final diagnosis was ACD-associated RCC. CONCLUSIONS ACD-associated RCC is a common tumor in patients undergoing long-term dialysis. When ACD-associated RCC is located in the renal pelvis, the imaging findings are similar to those of urothelial carcinoma. Therefore, it is important for radiologists to include ACD-associated RCC in the differential diagnosis.